1. Field of the Invention
The invention relates to an optical sensing apparatus, a filter apparatus, and a projector, and especially relates to an optical sensing apparatus, a filter apparatus, and a projector with anti-dust structure.
2. Description of the Prior Art
As the dependence on electronic equipment of people increases, the adaptability to environment of the electronic equipment is promoted. In general, a housing of electronic equipment generating heat has a plurality of vents formed thereon for air to pass through for taking away heat generated in operation by electronic components inside the housing. However, in some environments, such as arid zones, there is often fine dust floating in the air. The fine dust enters the housing with an air flow, and a part of the dust deposits on the surfaces of the electronic components. This situation does not matter for a general requirement of heat dissipation. But for an electronic component, such as an optical sensor, needing to sense exterior information, the sensing function of the electronic component is reduced or fails when a certain amount of dust deposits on the surface of the electronic component. Especially for an optical sensor for controlling rotation speed of a color wheel motor of a projector, once the optical sensor fails, the projector cannot work correctly any more.
Furthermore, because the rotation speed of the color wheel motor is quite high and the optical sensor for sensing the rotation speed of the motor is very close to the rotation surface of the motor, the air flow induced by the motor due to the rotation makes more dust deposit on the surface of the optical sensor. Besides, the rotation surface of the motor generates static electricity thereon due to high speed rotation, and the rotation surface attracts more dust easily so as to worsen the problem of the dust deposition on the surface of the optical sensor. Moreover, when the dust attracted on the rotation surface lies in the marks used by the optical sensor, the sensitivity of the optical sensor decreases so that the sensing function of the optical sensor is reduced, even to fail. When the color wheel motor and the optical sensor are sealed, the sealed structure can avoid dust but obstructs dissipating heat from the color wheel motor, which leads to instability of the rotation speed of the motor and projecting images with errors of color.